The genetic mechanism for induction of the metastatic phenotype was studied by using a) somatic cell hybridization or b) DNA transfection technique. a) Cell hybrids were derived from fusions of high (B16-F10) or low (UV-2237) metastatic tumor cells with tumorigenic (K1735-C116) or normal cells (macrophages). Metastatic and tumorigenic cell hybridization resulted in augmentation of both metastatic capacity and collagenase IV activity. Metastatic and normal cell hybridization yielded suppression of both the metastatic capacity and collagenase IV activity. This study shows that collagenase IV activity correlates with the metastatic capacity in nude mice and may therefore be genetically linked with other factors required for metastases. b) NIH/3T3 cells transfected with human tumor DNA containing an activated N-ras oncogene were metastatic in 100% of NIH nude mice recipients. NIH/3T3 cells transfected with an oncogene alone (V-Harvey-ras) produced metastases in 50% of the mice. The control and spontaneously transformed 3T3 cells were non-metastatic. Both transfected 3T3 cell clones secreted augmented levels of collagenase IV, and invaded human amnion basement membrane in vitro. The transfectants were sensitive to natural killer (NK) cell or macrophage cytotoxicity in vitro but were able to produce metastases in NK stimulated nude mice. Southern blot and slot blot analysis of genomic DNA from the human tumor DNA transfected cells and the corresponding lung metastases revealed a low level (two-fold) amplification of the N-ras specific DNA sequences in the metastatic DNA. Human repetitive (Alu) sequences were also demonstrated in both the transfected and metastatic cells. This work shows that metastatic properties can be conferred upon NIH/3T3 cells by transfection with either an isolated oncogene or genomic tumor DNA. 2) Human type IV collagenase was purified from culture media of metastatic melanoma cells with a molecular weight of 70,000.